Various dipeptides have been converted to their trifluoroacetylhexafluoroisopropyl and pentaflouropropionyl-hexafluoroisopropyl derivatives and analyzed under gas chromatographic conditions. The derivatives show good separation properties and can be separated on nonpolar or slightly polar columns. Dipeptidyl aminopeptidase I, which specifically splits polypeptides into dipeptides, has been prepared from beef spleen preparation to quantitative multiple ion detection mass spectrometry of neuropeptides.